Kirstie Scott lives at Half-Moon Ranch, where her mother runs a pony trekking centre. She has her own palomino pony and together they love riding the local trails. Storms, floods and earth tremors are all facts of life in this wild terrain, and at times the landscape itself proves the enemy to the horses and riders.

Watching a neighbouring rancher break in three new horses, Kirstie is horrified by her cruel treatment of one particularly strong-willed mare, Midnight Lady. In a desperate bid to free her, Kirstie pays a night-time visit to the ranch. But her plan backfires when not one, but eight horses escape and disappear into the mountains. Now Kirstie's in big trouble - should she own up? And if she does, will she ever see Midnight Lady again?